Recently, a structure composed of a fiber-reinforced resin is used in various fields particularly requiring high strength property and light property in weight. Although a fiber-reinforced resin can exhibit an extremely high strength and stiffness, it causes a local breakage because it causes a brittle fracture against an impact load. In fields where such breakage is not desired, by designing the structure so that an additional mechanism, for example, a member to connect the fiber-reinforced resin structure to another member, can be deformed or broken first, or so that an impact energy can be absorbed by the additional mechanism, breakage of the fiber-reinforced resin structure itself has been prevented. Namely, a mechanism for a safe brake or absorbing impact energy has been provided separately from the fiber-reinforced resin structure.
For example, although not limited to application to a fiber-reinforced resin structure, for a component for vehicles, a structure providing an external mechanism capable of absorbing an impact energy (for example, JP-A-2010-179753), a structure capable of absorbing an impact energy utilizing delamination at an adhesive layer (for example, JP-A-2009-208578) and the like are known.
In such a structure providing an additional mechanism, however, an additional component or an additional assembly step is required and, in particular, an increase in the production cost is caused from the viewpoint of the number of components or the assembly steps.
On the other hand, JP-A-2007-253733 discloses a structure wherein a fastening portion of a component for vehicles formed as a stacked body of fiber-reinforced resin sheet materials is formed so that a fastener bites into an interlayer part of the stacked sheet materials, and an impact load is absorbed by causing the stacked body to be delaminated at the interlayer part.
In the structure disclosed in JP '733, however, since it stands based on occurrence of deformation or breakage in the direction of the interlayer delamination which usually has a high possibility causing a fiber-reinforced resin structure to be most weakened in strength, there is a fear that it becomes difficult to make the fiber-reinforced resin structure exhibit the originally targeted high mechanical properties. Namely, it becomes a structure which sacrifices the originally targeted high mechanical properties.
Accordingly, paying attention to the above-described problems in conventional technologies, it could be helpful to provide a fiber-reinforced resin structure capable of absorbing external loads such as impact energy with extremely high efficiency via deformation or displacement only of a necessary local part without accompanying breakage, without increasing the number of components or assembly steps and while making the originally targeted structure exhibiting high mechanical properties.